Investigation of the role of the pif region of F-factors and cetain R-factors in the abortive infection of T7 in E. coli will be continued. Emphasis will be on the identification of the protein products of the pif region; analysis of the control of pif gene expression; genetic analysis of the pif region. The function of the pif protein products in preventing the translation of T7 late mRNA will be investigated. The role of host mutations on the expression of pif inhibition will be investigated. Mutations in host RNA polymerase, ribosomal proteins and DNA gyrase can have an effect on the expression of pif. We will determine the level of action of these host mutations on pif transcription or translation. The 70,000 Dalton Pif protein can now be recognized on polyacrylamide gels and pif specific mRNA can be measured by hybridization to specific DNA probes.